Researchers from the Faculty of Mechanical Engineering (Laboratory for Hydraulic Machines – LVTS), in collaboration with the Biotechnical Faculty, published the results of their research in the prestigious journal Water research (IF=13.4). They showed the effect of single micrometer-sized cavitation bubbles on the bacterial cells of Escherichia coli. They demonstrated that the cells in close proximity to the bubble are damaged, and at the same time estimated the hydrodynamic force for inactivating the bacterial cells by numerical analysis.

Cavitation is a physical phenomenon that describes the phase transition from liquid to gas and back to liquid at constant temperature. The formation and collapse of cavitation bubbles is responsible for the mechanical, thermal, and chemical effects of cavitation, which are used for various purposes, including the inactivation of microorganisms in drinking and wastewater. Despite numerous studies on inactivation of bacterial cells by cavitation, the fundamental understanding of the collapse of a single bubble, comparable to the size of a bacterial cell, is still unknown. Therefore, the researchers developed a system to generate single micrometer-sized cavitation bubbles using an optical tweezer system and a high-speed camera to visualize the rapid collapse of the microbubble. The system allowed them to observe the dynamics of microbubble collapse near the wall and near the bacterial cells. Fluorescence microscopy allowed them to determine the damaged cells.

Figure 1: Graphical abstract

The results show that the collapse of the microbubbles leads to detachment or damage of the cells when they are in close proximity to the collapse of the microbubble. Additional numerical investigations revealed the formation of a microjet as a possible mechanism of cell damage. Using the experimental and numerical results, the researchers determined the peak hydrodynamic force required to damage a single E. coli bacterial cell.

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